Process for the production of iron oxide



Feb. 12, 1946.l J. W. AYERS 2,394,579

PROCESS FOR THE PRODUCTION OF IRON OXIDE Filed June 8, 19:59 2sheets-smeet 1 WOnU WQ QSA vom, mi

J. W. AYERS Feb. 12, 1946.

PROCESS FORl THE PRODUCTION OF IRON OXIDE Filed June 8, 1939 2Sheets-SheetI 2 INVENTOR JOSEPH VV. AYEQS ff f BY me ATTORN EYS PatentedFeb. 12', 1946 2,394,579 PROCESS FOPv THE PRODUCTION OF IRON OXIDE IJoseph W. Ayers, Easton, Pa;, asslgnor to C. K.

Williams & vania Co., a

corporation of Pennsyl- Application June 8, 1939, Serial No. 278,028

Claims.

This invention relates to a new and improved process for producing rediron oxide and particularly to a new cyclical process for producing rediron oxide from ferrous sulfate.

Pure red iron oxide is one of the principal colored pigments used by thepaint, rubber, linoleum and similar industries.

The process generally employed for the manufacture of iron oxidepigments involves the calclnation or thermal decomposition of ferroussulfate in a large rotary kiln. The usual kiln is a large, inclined,cylindrical tube lined with refractory material. The size of the kilnvaries.y from 50 to 100 feet in length and from5 to 10 feet in diameter.Ferrous sulfate is charged into the elevated end of the kiln and passesby-gravity through the entire tube during rotation, to be discharged atthe lower end. A flrebox is located adjacent the lower end of the kiln,and heat and gases from the combustion of coal, coke, gas or oil in thisreboX sweep through the kiln in contact with the ferrous sulfate andexit through a flue at the upper end of the kiln.

The ferrous sulfate crystals to be used in the production of iron oxideare sometimes obtained from scrap iron by a series of treatments thatresults in FeSO4.H2O as the end product. The

iron is dissolved in a dilute sulfuric acid solution.

The solution is then crystallized to form FeSO4.7H2O

which may be separated from the mother liquorin a centrifuge. The WetFeSO4.7H2O crystals are dried and then dehydrated to obtain FeSO4.H2O

in a condition suitable for the decomposition process.

The calcination or decomposition of the ferrous sulfate in the rotarykiln involves treatment of the material under indefinite conditions asto temperature and in the presence of an atmosphere consisting ofcombustion gases and an in determinate amount of a-ir. In order tosecure suiliciently high temperature in the upper or inlet end of thekiln, the lower or exit end must often be overheated. In practicedecomposition is allowed to proceed until most of the ferrous sulfatehas been converted to ferrie oxide, which may take place, at leastpartially, according to the reactions:

The calcined material issuing from the lower end of the kiln is washedto remove soluble impurities, whereupon substantially pure red ironoxide suitable for use as a color pigment may be obtained. Thedecomposition gases exhausted 5 from the upper end of the kiln consistof combustion gases, water vapor and a very small concentration ofsulfur oxides. These gases are generally wasted inthe air.

This common process for producing red iron oxide has a number of defectsand shortcomings that have not been overcome prior to my invention. Whentreating the usual ferrous sulfate, which contains from .15 to .50% ofmanganese sulfate as an impurity, it is impossible to obtain a highpercent conversion of ferrous sulfate to ferrie oxide while securingiron oxide sulciently free of manganese oxide to be of satisfactorypigment quality with respect to manganese'oxide Y content and colorproperties. When producing valuable iron oxide pigments with lowmanganese oxide content the yields do not exceed about 70%. Also, it isdiiilcult to vary the color properties of the product accurately; andthe efliciency of the process with regard to heat consumption,appationably low. y

A new and improved process overcoming these and other shortcomings ofthe conventional process is disclosed and claimed in my copendingapherewith. v

Another lobjectionable feature of the conventional process for producingred iron oxide resides in the lack of eilicient utilization of processmaterials and by-products. The decomposition gases from the calcinationkiln. for example, are of such nature that recovery of their valuableconstituents is economically impracticable, so that these gases` areusually entirely wasted. This not only involves an economic loss, but italso frequently results in contamination of the air in the neighborhood0f the place where the process is being operated. Yet it would entailexcessive costs to operate the process with special provision forpreventing the release of the kiln gases into the air.

It is therefore an object of the present inven-l ratus and materialrequirements, etc., is objecplication, Serial No. 278,027, vled of evendate eiilcient production and utilization of materials avoided, and inan economical and practical manner.

yA further object of the invention is to provide such a process which atthe same time overcomes the above mentioned defects and shortcomings ofthe conventional process for producing red iron oxide, giving a highconversion yield of iron oxide of high quality and low manganese oxidecontent, enabling ready control over and variation of color propertiesof the iron oxide, and resulting in materially increased efficiency ofprocess operations.

One of the features of the present invention consists in carryingout'the decomposition of ferrous sulfate, in the production of red ironoxide, under closely controlled temperature conditions and in supplyingto the decomposing material a regulated stream of air or other gas in anamount sufficient to obtain the desired quality and yield of iron oxidewhile restricting the supply of air or other gas so that thedecomposition gases include, comparatively, a very high concentration ofsulfur oxides. The decomposition gases are then treated economically toconvert sulfur oxide contained in them into sulfuric acid, which may becirculated advantageously to a starting point in the process and used inthe production of ferrous sulfate from scrap iron or the like. l

Another important feature of the present invention resides in carryingout the decomposition of the ferrous sulfate in such manner as to obtaina relatively'high percentage of sulfur trioxide in the sulfur oxidespresent in the decomposition gases. This is accomplished in part bysupplying air or other oxygen containing gas in an amount suicient .tosupport decomposition of the ferrous sulfate according to the reaction:

which results in the liberation from the decomposing material of gasesthe sulfur oxide ccntent of which is substantially all sulfur tri-oxide.

The sulfur tri-oxide generated according to this reaction is preservedto a large extent, notwithstanding the strong tendency of sulfurtri-oxide to decompose into sulfur dioxide and oxygen at thetemperatures encountered in the process, by maintaining appropriatecontrol over the maximum heating 'temperatures in the zone Whereconversion of ferrous 'sulfate is taking place, and

economic loss and the atmospheric contamina tion caused by the releaseof decomposition gases according to the prior process, and atrthe sametime 'results in economies, improvements in product quality and yieldand savings `that are not obtainable from the prior process.

Other features and advantages of the invention will appear from thefollowing detailed description of a preferred embodiment when consideredbyhastening the ow ofthe decomposition gases A from this hot zone. l

According to the present process, I may produce decomposition gasescontaining more than 10% of sulfur oxide, in which more than 50% of thesulfur oxide content consists of sulfur trioxide. These gases areconveniently and economicaliy flowed through a system for the recoveryof their sulfur values, in which the sulfur tri-oxide may b e convertedto sulfuric acid by absorption in water and in which the remaining Ysulfur dioxide may be converted to sulfuric acid by the well knowncontact or catalytic process. The sulfuric acid recovered from the gasesmay then be passed to the starting point of the process and used for thedigestion of iron to produce ferrous sulfate. 'I'he gases remainingafter extraction of sulfur oxides may be released into the air withoutdanger of contaminating the surrounding atmosphere.

The preferred embodiment of the invention is a cyclical process for theproduction of red iron oxide which results in maximum utilization ofprocess materials and by-products, eliminates the in connection' withthe accompanying drawings, in which:

Figure 1 is a diagrammatic flow chart indicating the paths of flow andthe treatment of materials in the practice of the process;

Figure 2\ is a vertical longitudinal section through one form of rotarymuiile which may be employed in carrying out'the calcination ordecomposition of the ferrous sulfate;

Figure 3 is a fragmentary end view of the mufile, viewed from the righthand end of Figure 2; and Y Figure 4 is a vertical cross section throughthe muie, approximately along the line 4 4 of Figure 2.

Referring particularly to Figure 1 of the drawings for illustrativedetails of a preferred embodiment, scrap iron or other suitable ironmaterial is introduced into a digesting tank containing dilute sulfuricacid, and the iron is digested and dissolved in the acid to form asolution of FeSO4.'7I-I2O. This solution is passed into a crystallizerwhere the hydrated ferrous sulfate is crystallized. The-resultingmixture of crystals and mother liquor is separated, for example, in

a centrifuge, the mother liquor being recirculated to the digestingtank, as indicated in Figure 1, so

that none of its ferrous sulfate content is lost l from the process. Thewet FeSO4.'7Ha0 crystals are`passed through a drier for the removal oi'water and then through a dehydrator `where water of crystallization isextracted, in a well known manner, to produce FeSO4.H2O in a conditionsuitable for conversion to ferrie oxide.

The ferrous sulfate from the dehydrator is then passed into the calcinerto be converted into iron oxide.

other suitable'refractory material, which provides an elongated heatingchamber i2 through which extends a rotary muille 30 for carrying out,the decomposition of the ,ferrous sulfate. end portions'of the munie 30project through and beyond oppositelg disposed openings Il and I6 in thefurnace walls. A plurality of combustion chambers i8 are located in thelower portionof i the furnace, and the muilie is heated to controlleddecomposition temperatures by the combustionV of suitable fuel fromburners 20,' which extend into the combustion chambers I 8. l

'I'he entire-muille is mounted for rotation at a ,suitable speed, forexample, by means of tires 32 and 34 secured to the mufile wallandcooperating rollers 36 and 38. Its axis of rotation is slightly inclinedso that material introducedinto If desired, it may be coated or mixed ywith a small amount of an oxidation-*retarding catalyst, such as aninorganic alkali metal salt,V

Opposite Y the mulle at its upper end gradually progresses to the lowerend during rotation.

In order that the composition of gases supplied to and exhausted fromthe mutlle may be conganese oxide content of the nal iron oxide productand on the desired rate of conversion of the ferrous sulfate to ironoxide. The ferrous sulfate from the dehydrator is fed into the dischargeheader 4.0 at a regulated rate, from which it trolled, the muilie ismade substantially gas-tight, 5 passes through the mulile tubes 42 insubstantially ,p while providing suitable means for feeding and uniform,evenly distributed streams. At the same discharging solid materials andfor introducingTA time, air or other oxygen-containing gas is inanddrawing oi gases. troduced into header 40 and into the muille tubes Asillustrated, the main body cf the munie eomfrom supply pipe 5,4- Thesupply of gas is regprises a charge header 4U at its upper end, a 10ulated to provide an amount of oxygen sufdcientmultiplicity of elongatedtubes 42 extending to support decomposition and conversion of thethrough furnace chamber l2 and all commumferrous sulfate to ferrie oxideaccording to the eating with the charge header, and a common reaction:discharge header 44 communicating with the out- ZFESO 1 O2=Fe O 250321,120 let ends of tubes 42 and hatving 1neans tilerein gir l5 This gassupg/zhoweve s; resul-cmd that 'h 'f l' maeria from emue 1 lll-nclhgsontso 1d the decomposition gases exhausted from the heat- The ferroussulfate may be fed into the charge ing Z011@ 0f the mum@ and drawn 011'through pipe header 40 by suitable feeding means, for example, 56Contain 9" comparatively high 001196111512303 an axially disposed screwconveyor 50 opening 20 Usually about 12 120 15%, 0f Sulfur Oxides. intoheader 40 through a port in a stationary end By Virtue 0f the highlyemcem? transfer 0f Wan section 52 Air or other gas may be introheat tothe ferrous sulfate in the muile tubes, duced into header 40 by means ofa supply;1 pipe gi Isfsm ptfetonlglenerl i cf' idoognumcatmg with aSecond port n Wa se course of the treatment are kept at the lowest Theferrous sulfate accumulated in -charge possible point for thePl'QductiOn 0f Fach Darheader an is picked up in the inlet ends of theictulal; fade gf iron lime-h lllrtflllerfre, the several muille tubes 42during rotation of the a e 0. 0W 0 gases 011g Ae e9 11g Zone mull'le,and the material continuously progresses 0f the mume is enlanced and thelingering 0f lengthwise of the tubes, and through the reactiongfclcgglugisp il S112 zone mau-named therem by heat from the fupmaximumextent consistent with other requirenace, until 1t is finally dischargedfrom tubes 42 t f th b i 1 into header 44. The calcined materialentering men sfo t e process f Y prov ding me Void the discharge headeris lifted and dropped to- Spam? or he passage 0 gases through the C011'Ward the axis of the mume by radial vanes 55 35 Version zone of themullle. In this manner I which rotate with the munie. An axiallydisposed Doduce from the calculation, Stage 0f the PIO@ discharge cone58 directs the material through a essddeconosiltjorgs mfvlch Ilorethiac'n 50% discharge opening 60 and thence into a stationlt fiflath ais covsigts oslulrotril; gtlilgog ,.gattizttgstlgreg lrlbstla At thesame me, conversion of the ferrous sui. 62 the maera] may be Withdrwn asdesired by fate into red -iron oxide of high quality is car. means ofsealed discharging means, such as a roietd out at; glve traordmaruyyields of tary star wheel 64. `Decomposition gases exe Weed anta t Zooronge a manga? hausted f rom the muflle may be drawn oil through nengagmeng 'mchart in Figure 1 antgtlegfeglgg 1333255122 asfil'hw, of thedrawings, the decomposition gases from trated are arranged in paralleland circularly the calcination apparatus are passed through a l systemfor the production of sulfuric acid, which spaced relation around theaxis of rotation of may include a unit of Wen known type mdb smbtssggtfgllmrggrg cated at A, for the con'version of sulfur tri-oxide 1 intosulfuric acid by absorption and another unit atei-al in cross section,as indicated, for example, .of Wen known type indicated at B for the cond m Figure with such a construction the ma' version of sulfur dioxideinto sulfuric acid by terial passing through the tubes is continuallythe contact or catalytic process When sulfur turned over and overduring. its progression from tri-oxide exceeds 50% of the sulfur oxideconge sargf heeg H drlrsll' h'lde igt; tent of the gases, as in thepreferred practice of degom rsstrog zoe taies imc at mgxmml ef theinvention, it may be desirable in some cases i p F tfeh t f to convertonly the sulfur tri-oxide intq sulfuric c ency' or e ec lveness o eatrims er the acid provided that lt is satisfactory to` release muilietubes are preferably made entirely of sheet 6o the emaimng gases intothe an, metal, and high strength and corrosion resist- The sulfuric acidobtained in this recovery vx'lgle areoglamiitgyolfnennilentlhi ligesssystem is passed 'into the digesting tank at the a6 r p s head of theprocess, either directly or after stor- Ject to Contact Wlth materialsand gases at hlgh ege where it is used-fer digesting the incomingtemperatures, from strong, corrosive-resistant, 65 not; p ncreep-resistant metals such as the high chromium Tile calcined 'materialdischarged from the irons and Steels anoyfd in smaller percentagescalcination apparatus consists principally of iere with metals such asnickel tungsten manganese ric oxide with a small lpercentage of ferriesula'nd molybdenum' fate. This material is passed to the thickener Inthe practice of the present process, the heaiiwhere it is washed withwater to dissolve soluble mg temperatures for the material inthe mum@sulfate and where the residual insoluble ferrie tubes are kept atclosely regulated points between oxide is partially separated from theresulting about 1300 O 1 550" F. The particular tempera- 301111-,101'1aThe ferric sulfate 50111131011, as inditure will depend upon the desiredcolor and mancated in Figure 1, may then be flowed to the digesting tankto be reduced to ferrous sulfate by the iron there present, and then tobe recirculated through the process. Ferrie oxide separated at thethickener is filtered, dried and dispaints, rubber, linoleum and thelike.

For purposes of clarity and illustration I have described numerousdetails of a preferred embodiment of the present invention and havedescribed and illustrated details of construction of a form of apparatuswhich isparticularly suitable for use in practicing the invention. Itwill be understood, however, that various features'rof the process maybe modied or avoided without sacrificing contributions of the inventionand that the process claimed herein may be practiced with various typesof apparatus. I therefore desire that the invention be accorded a scopefully commensurate with its novel teachings as limited only by the fairrequirements of the appended claims.

I claim: v v

1. In a process for producing red iron oxide, the steps which compriseheating ferrous sulfate out of direct contact with ame or combustiongases in a substantially closed heating zone to temperatures between1300 and 1550 F. to cause conversion of ferrous sulfate into iron oxideof a predetermined quality, supplying air to the decomposing material in an amount suicient to support the reaction2FeSO4.H2O+1/2O2=Fe2Oa+2SOs-l-2H2O restricting the supply of air so thatthe gases v exhausted from the heating zone contain at least restrictingthe supply of air so that the gases exhausted from the heating zonecontain at least of sulfur oxides, limiting the time of conrestrictingthe supply of air so that the gases exhausted from the heating zonecontain at least 10% of sulfur oxides, limiting the time of contact tactof suchY gases with decomposing conditions in the heating zone such thatthe gases have at least 50% of sulfur tri-oxide in said sulfur oxidecontent and converting sulfur oxide from said gases into sulfuric acid.

3. In a process for producing red iron oxide, the steps which comprisepassing ferrous sulfate continuously through a substantially closedheating zone heated externally to temperatures between 1300 and l550 F.to cause conversion of of such gases with decomposing conditions in theheating zone by restricting the volume of gases held in said zone vsothat the exhausted gases have at least of sulfur tri-oxide in saidsulfur oxide content and converting sulfur oxide from said exhaustedgases into sulfuric acid. I

4. A cyclical process for producing red iron i oxide which comprisesdissolving iron in dilute sulfuric acid, crystallizing and separatingFeSOiJHzO from the solution, drying and dehydrating the FeSO4JlH2O toobtain FeSO4.H2O, decomposing the FeSOi.HnO by heating the sameindirectly in a substantially closed heating zone to a temperaturebetween 1300 and 1550 F.`While supplying air in an amount at leastsumcient to support decomposition according to the reaction furic acidina tank, crystallizing and separating' FeSOiHHrO from the solution,returning the FeSO4J7H2O mother liquor into said tank, drying anddehydrating the FeSO4.7HzO to obtain FeSO4.H2O, producing decompositiongases containing at least 10% of sulfur oxide and calcined materialconsisting essentially of ferrie oxide and ferric sulfate by heatingindirectly and decomposing the FeSO4-H2O out of contact with flame orcombustion gases, in an externally heated mufile, While supplying arestricted amount of oxygen-containing gas to the decomposing mate- Arial, fixing the conditions of decomposition such that atleast half ofthe sulfur oxide content of said gases is sulfur tri-oxide, convertingsulfur oxide from said decomposition gases into sulfuric acid, flowingthe resulting sulfuric acid into said tank, washing said calcinedmaterial to obtain ferrie sulfate .solution and wet ferric oxide, ilow'ing the ferrie sulfate solutioninto said tank, and drying the ferrieoxide to obtain substantially pure iron oxide. v

JOSEPH W, AYERS.

